One of the problems associated with operation of trailer trucks in the tendency of the tractor and attached trailer to jackknife under certain conditions. Tractors and trailers are conventionally coupled together by a fifth wheel on the trailer in which a kingpin secured to the trailer is pivotally received. This coupling enables the tractor to pull the trailer and provides for relative pivotal movement for maneuvering the vehicle. Jackknifing occurs when the trailer pivots relative to the tractor to an extent such that the operator can no longer maintain or recover control over the vehicle. Typical driving conditions which may cause jackknifing are those in which the tractor wheels are made to lock and slide or to spin; in either case, the direction of the wheel can no longer be controlled, and it takes the path of least resistance. Improper braking or steering and accelerating or decelerating too fast can all cause jackknifes, especially on roads made slick by rain, snow, or ice. Anti-jackknifing arrangements have been developed to prevent or minimize jackknifing action by limiting the allowable pivotal movement between the tractor and trailer.
Various anti-jackknifing devices for installation on trailer trucks are disclosed in prior patents. In general, these devices include a first stop retractably mounted on either the fifth wheel or on a wear plate under the trailer and a pair of cooperative stops mounted spaced apart on the other of these members. The pair of stops limit pivotal movement beyond a predetermined angle when engaged by the first stop. U.S. Pat. Nos. 4,556,232, issued Dec. 3, 1985, to Server; 4,585,248, issued Apr. 28, 1986, to Miller et al.; and 4,120,514, issued Oct. 7, 1978, to Sanders, disclose arrangements wherein an auxiliary pin is mounted on the fifth wheel and is deployable upward so as to be positioned in an arcuate slot in the wear plate under the bottom of the trailer. Pivotal movement of the tractor in these devices is limited by the length of the slot, the pin being stopped when it engages an end of the slot. U.S. Pat. No. 4,119,330, issued Oct. 10, 1978, to Capps, discloses the use of a pair of spaced abutments on the fifth wheel and a movable stop on the trailer. U.S. Pat. No. 3,895,827, issued July 22, 1975, to Padrick, discloses mounting of a stop block on the fifth wheel platform for movement upward into an arcuate recess at the periphery of the wear plate on the trailer, stopping action occurring by engagement of the block with the edge defining an end of the recess. The devices disclosed in these patents include features such as a pneumatic or hydraulic cylinder and suitable linkage for deploying and retracting the stop in and out of its operating position.
Prior anti-jackknifing arrangements as discussed above present a disadvantage in that they require cutting into the fifth wheel and/or the wear plate of the trailer in order to provide necessary slots or recesses for operation of the movable stop member. This requirement makes installation of the apparatus on the fifth wheel and trailer plate difficult, and the resulting slots or recesses substantially reduce the strength of the plate or fifth wheel, creating weak points susceptible to failure. It would be desirable to provide anti-jackknifing apparatus that may be installed on existing trailers and fifth wheels by means such as welding without cutting slots or recesses in existing structural members. Apparatus with such features is disclosed in my co-pending application, referenced above. That apparatus included a brick-shaped latch block deployable from a stowed position below the fifth wheel and engageable when deployed upward with similarly shaped stop blocks secured to the bottom of the wear plate of the trailer. In this apparatus, flush contact of the end of a stop block is made by a side of the latch block adjacent to its forward end when deployed. This arrangement proved unsatisfactory when undergoing tests in that the deployed latch block end, when subjected to the severe forces encountered in an actural jackknifing situation, was sprung downward out of position and past the stop block, thus allowing the trailer and tractor to jackknife. Structure that provides for interlocking of the engaging blocks so as to prevent failure due to being sprung out of position is therefore required.
Other features needed for optimum use of such apparatus include a means for automatically disabling the system at low speeds to enable routine turning of the truck and means for monitoring and recording a history of occurrences of activation and deactivation of the system.